A conventional common injection molding machine molds a molding product by sending granular thermoplastic resin, which is a raw material, into a heating cylinder, sending out resin using a screw provided inside the heating cylinder and movable forward/backward, to a nozzle at an end of the screw while melting the resin, causing the melted resin to be injected from the nozzle provided at the end of the screw into a cavity of a mold, causing the melted resin to cool and solidify in the cavity, then opening the mold and removing a molded product stuck to the mold from the mold using a protruding pin or the like.
Such an injection molding machine for molding a molding product such as plastics is generally constructed of a mold clamping unit and an injection unit, and the mold clamping unit is generally provided with a mold including a fixed mold and a movable mold, the movable mold is made to move forward/backward to/from the fixed mold through movable means capable of mold clamping such as a toggle mechanism or straight hydraulic scheme and the mold is thereby closed or opened during mold clamping.
An injection unit is used when pellet, which is granular resin is supplied as melted resin into the cavity formed during mold clamping of the aforementioned mold, and this injection unit is provided with drive means such as a motor as the drive source, the torque of the motor is sequentially transmitted via a pulley, belt or the like, the screw in the heating cylinder is rotated by a ball screw mechanism that converts rotary motion to linear motion, the melted resin is thereby transferred, and the melted resin is then injected from the nozzle into the cavity between the molds provided in the mold clamping unit.
Furthermore, Patent Document 1 discloses a runner-less mold that provides a recessed part in the center of a fixed mold, which is one of the fixed mold and a movable mold that make up a cavity, provides a compression core that engages with this recessed part in the center of the movable mold in a manner movable forward/backward, causes an end of a hot nozzle inserted in the fixed mold to protrude in the center of the recessed part, forms a runner section that is opened/closed by the compression core between the recessed part and compression core and leaves a resin layer in the recessed part when the compression core moves forward.
[Patent Document 1] Japanese Patent Laid-Open No. 8-281714